1. Field of the Invention
The present invention relates to an illuminating apparatus for a display device and a display device having the same, and specifically relates to a display device having a plurality of illuminating units each of which includes a first feeding member, a second feeding member, and a cold-cathode tube lamp to which power is supplied from a power supply apparatus via the first and second feeding members, the equivalent circuit of each of the illuminating units being a series combination of a negative resistor and a capacitor connected to an end of the negative resistor.
2. Description of the Related Art
Since typical cold-cathode tube lamps used as a light source for display devices have a non-linear negative impedance characteristic, they cannot be driven in parallel. Thus, power supply circuits are normally provided one for each cold-cathode tube lamp. This, however, requires as many power supply circuits as cold-cathode tube lamps causing cost increases. This is disadvantageous also in terms of downsizing, weight reduction, and cost reduction.
Examples of a lamp in which the above problems are solved include the cold-cathode tube lamp disclosed in a patent application that has already been filed by the applicant of this application (see WO2006/051698A1). A circuit formed of a first feeding member, a second feeding member, and a cold-cathode tube lamp of WO2006/051698A1 to which power is supplied from a power supply apparatus via the first and second feeding members, whose equivalent circuit is a series combination of a negative resistor and a capacitor at least at one end of the negative resistor, has a nonlinear positive impedance characteristic; thus, the lamp disclosed in WO2006/051698A1 can be turned on in parallel by being driven in parallel.
In addition to an illuminating unit formed of a first feeding member, a second feeding member, and a cold-cathode tube lamp to which power is supplied from a power supply apparatus via the first and second feeding members, its equivalent circuit being a series combination of a negative resistor and a capacitor connected to one end of the negative resistor and a capacitor connected to the other end of the capacitor, WO2006/051698A1 discloses an illuminating unit formed of a first feeding member, a second feeding member, and a cold-cathode tube lamp to which power is supplied from a power supply apparatus via the first and second feeding members, its equivalent circuit being a series combination of a negative resistor and a capacitor connected to one end of the negative resistor.
In an illuminating apparatus for a display device incorporating more than one of the latter illuminating unit, that is, the illuminating unit formed of a first feeding member, a second feeding member, and a cold-cathode tube lamp to which power is supplied from a power supply apparatus via the first and second feeding members, its equivalent circuit being a series combination of a negative resistor and a capacitor connected to one end of the negative resistor, when, as shown in FIG. 8A, capacitors C1 to C4 which are components of the equivalent circuits 11 to 14 of the illuminating units, respectively, are disposed in the same position, even if the phase of a voltage outputted from one end of a power supply apparatus 15 and the phase of a voltage outputted from the other end of the power supply apparatus 15 are substantially 180 degrees inverted to each other, the voltage at an end portion of each of the resistors R1 to R4 at a side thereof to which a capacitor is connected is lower than the voltage at an end portion of each of the resistors R1 to R4 at a side thereof to which no capacitor is connected. This reduces the brightness at the side where capacitors C1 to C4 are disposed, and increases the brightness at the side where the capacitors C1 to C4 are not disposed as shown in FIG. 8B, and as a result, the brightness gradient in the tubular axis direction of the lamps becomes quite high. When, as shown in FIG. 8A, the capacitors C1 to C4, which are components of the equivalent circuits 11 to 14 of the illuminating units, respectively, are disposed in the same position, noise and sounding occur in a concentrated manner at the same position, which is not preferable.